One year ago, tragedy struck the Miami suburb of Surfside, Florida. As residents of the Champlain Towers South slept, the 12-story oceanfront condominium collapsed: first the pool deck, then the central section and eastern wing. 98 people died.
The disaster didn’t happen overnight. Investigations have revealed that residents and maintenance personnel had noted concerns about the building’s structural integrity in the years leading up to the collapse. Corrosion of steel reinforcement within the in-ground concrete foundation elements, car park concrete elements, and swimming pool concrete elements is considered to be a significant contributory cause of the collapse.
Following the Surfside tower collapse, AMPP formed a Task Force of renowned experts in corrosion of concrete structures to engage in analysis of the Champlain Towers disaster. The panel is focused on fast-tracking standards revisions, guidelines, and training requirements to improve inspection, evaluation, and ensuing repairs of concrete structures.
The task force will provide supporting information to local, state, and federal officials, and those tasked with investigating this disaster at the National Institute of Standards and Technology (NIST).
In a recent op-ed, Linda E. Marquez, AMPP Surfside Collapse Task Force Chair wrote, “Corrosion isn’t just a nuisance or a cost of doing business. It should be viewed as a grave warning. Decisions should be based on best practices and technical standards, not finances. Painting over corrosion or patching repairs doesn’t increase asset integrity or sustainability. These actions might make a building more aesthetically pleasing, but they do not increase safety and in some instances may contribute to further deterioration.”
Reinforced concrete is a ubiquitous building material, favored for its versatility and low cost. The combination of concrete and steel gives structures the compressive strength of concrete and tensile strength of steel. However, disintegrating and deteriorating concrete is a major issue contributing to infrastructure issues worldwide. According to a report by the American Concrete Institute, “reinforced concrete … is vulnerable to corrosion, especially when subjected to cycles of wetting and drying that is often prevalent in highway bridges and parking structures exposed to deicing or anti-icing salts, and in structures located in marine environments.”
How does this corrosion process occur? Carbon steel reinforcement in contact with concrete develops a thin passive oxide layer that protects it from corrosion. However, this protective layer may be lost or compromised if the pH of the concrete pore solution falls because of carbonation or if aggressive ions such as chlorides penetrate to the steel reinforcement surface.
As the rebar corrodes, the corrosion products on the rebar take up more volume than the rebar alone. This causes stress in the concrete that results in cracks — which then allow more water penetration, accelerating the corrosion even more if required maintenance is not done.
A proactive approach to corrosion management is essential, says Marquez. “Including a corrosion expert as part of an inspection team can identify issues early so that mitigation strategies can be employed. This is a more cost-effective way to extend the life of a structure, and can help avoid the need for expensive repairs.”
There are several approaches to mitigate, prevent, or repair concrete corrosion. The traditional method of concrete repair is to remove the cracked and degraded concrete to fully expose the rusted reinforcement. All corroded material is removed and the steel is either treated or replaced before replacing with concrete mortars. Modern repair mortars are modified with a polymer to improve adhesion and resist the ingress of contaminants. Coatings are commonly used in combination with patch repairs to further reduce advancing carbonation and chlorides.
Additionally, cathodic protection is used to slow the rate of corrosion and mitigate further damage, either via anodes or with an impressed current cathodic protection system.
“Our core mission is to protect the public,” says Marquez. “Today, we can think of nothing more critical than working with our members to ensure a catastrophic event like the one in Surfside does not happen again.”
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Sources and Additional Reading
AMPP/NACE Standards relating to corrosion of reinforced concrete.
Australasian Corrosion Association. "Correcting Concrete Corrosion." Materials Performance Magazine, May 2020.
National Institute of Standards and Technology. "June 15, 2022, Update on the NIST Champlain Towers South Investigation."
Roberge, Pierre R. "Corrosion Basics: Corrosion Damage in Reinforced Concrete." Materials Performance Magazine, April 2021.
Whitmore, David and Matthew Miltenberger. "Galvanic Cathodic Protection of Corroded Reinforced Concrete Structures." Materials Performance Magazine, May 2020.